The present invention relates to acoustic wave sensors, and more particularly to a time-interleaved method for efficient operation of an acoustic wave sensor array for detecting parameters of interest, such as chemical concentration, pressure, humidity, temperature and the like.
Acoustic wave devices, such as surface acoustic wave (SAW) devices, thin film resonators, quartz crystal microbalances and the like, may be used as sensors for chemical and physical detection by coating them with materials sensitive to a parameter of interest, as disclosed in U.S. Pat. No. 4,312,228 issued Jan. 26, 1982 to Henry Wohltjen entitled "Methods of Detection with Surface Acoustic Wave and Apparati Therefor" incorporated herein by reference. Interaction of an acoustic wave with the sensitive material causes a change in the propagation characteristics, such as phase and velocity, of the acoustic wave. Operation of the resulting acoustic wave sensor as an oscillator is a method used for measuring these changes in the acoustic wave propagation characteristics.
A multiplicity of parameters may be measured by using an array of acoustic wave sensors in which each sensor of the array is coated with a different material with unique sensitivity properties. Prior systems of acoustic wave sensor arrays, as described in the 1993 article by Jay W. Grate et al in Analytical Chemistry, vol. 65, pgs. 1868-1881, entitled "Smart Sensor System for Trace Organophosphorus and Organosulfur Vapor Detection Employing a Temperature-Controlled Array of Surface Acoustic Wave Sensors, Automated Sample Preconcentration, and Pattern Recognition" incorporated herein by reference, have used a multiplicity of oscillator circuits with each oscillator driver dedicated to its own acoustic wave sensor. Some of the disadvantages of this approach are excessive power consumption due to each oscillator requiring as much as one Watt of power, excessive self-heating of the acoustic wave sensors as significant power may be dissipated in each sensor, inadvertent frequency locking of oscillators due to coupling between oscillators, and large component count and circuit board space for multiple oscillator circuits.
For field use, as opposed to research or laboratory use, it is desirable to have a measurement instrument that may be readily held in one's hand. To accomplish this it is desired to reduce the power consumption and the parts count as well as to prevent frequency locking between oscillators so each acoustic wave sensor in an array responds independently from the others.